We plan in healthy volunteers to characterize for E2020: the single oral dose peripheral and central compartment (P.&C.C) pharmacokinetic profile; the P.&C.C steady state, pharmacokinetic profile of 5 mg and 10 mg dosages; the terminal phase pharmacokinetic profile (last dose at steady-state); the magnitude and duration of plasma and CSF acetylcholinesterase (AChE) inhibition. We hypothesize that: E2020 will cross the blood-brain barrier with sufficient penetration to achieve measurable levels in the CSF and inhibit AChE; peripheralplasma E2020 and metabolite concentrations and markers of cholinesterase inhibition will correlate with CSF AChE activity.